restored comment

lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java

@@ -669,32 +669,31 @@ private <C extends Collector, T> T search(
               "CollectorManager does not always produce collectors with the same score mode");
         }
       }
-      final List<FutureTask<C>> listTasks = new ArrayList<>();
+      final List<FutureTask<Void>> listTasks = new ArrayList<>();
       for (int i = 0; i < leafSlices.length; ++i) {
         final LeafReaderContext[] leaves = leafSlices[i].leaves;
         final C collector = collectors.get(i);
-        FutureTask<C> task =
+        FutureTask<Void> task =
             new FutureTask<>(
                 () -> {
                   search(Arrays.asList(leaves), weight, collector);
-                  return collector;
+                  return null;
                 });
 
         listTasks.add(task);
       }
 
       sliceExecutor.invokeAll(listTasks);
-      final List<C> collectedCollectors = new ArrayList<>();
-      for (Future<C> future : listTasks) {
+      for (Future<Void> future : listTasks) {
         try {
-          collectedCollectors.add(future.get());
+          future.get();
         } catch (InterruptedException e) {
           throw new ThreadInterruptedException(e);
         } catch (ExecutionException e) {
           throw new RuntimeException(e);
         }
       }
-      return collectorManager.reduce(collectedCollectors);
+      return collectorManager.reduce(collectors);
     }
   }
 

lucene/core/src/java/org/apache/lucene/search/SliceExecutor.java

@@ -52,6 +52,7 @@ final void invokeAll(Collection<? extends Runnable> tasks) {
   }
 
   boolean shouldExecuteOnCallerThread(int index, int numTasks) {
+    //Execute last task on caller thread
     return index == numTasks - 1;
   }
 }